Agriculture Reference
In-Depth Information
Some experts suggest that control of black measles can be achieved with use of liquid
lime-sulfur applied after pruning. However, you must get the product into the cracks and
crevices of the vine, as well as into any cuts or pruning wounds, to attack the fungal fruit-
ing bodies. Other treatments include use of wax or tree tar to fill pruning wounds or other
holes. Though this method is still experimental, there would be no way for the fungus to
reinfect the vine if these holes are plugged up.
Black Rot
Guidnardia bidwellii
Black rot is caused by a fungus that overwinters in mummified fruit on the vine or
the ground. When fungal spores are released during spring rains, leaves may be reinfec-
ted. Brown circular lesions appear on the leaves with small black dots within the lesions.
Shoots, cluster stems, and tendrils may also develop lesions. Fruit can be infected during
blooming and eventually turns dark brown before shriveling into raisinlike mummies.
CONTROL
Timing of fungicide is critical: from just before bloom to up to a month after bloom.
However, copper and sulfur are not very effective against black rot, so good vineyard san-
itation is called for. Remove mummified fruit, especially any that is hanging on the vine,
and clear up infected leaves and canes. Do not compost the material.
Bunch Rot
Botrytis cinerea
This fungal disease, also called botrytis or gray mold, can grow on any plant material,
but mostly on young shoots or flower parts, on stressed or ripened fruit, or on dead (yellow)
leaves. This disease damages ripened fruit and can account for severe losses. Zinfandel
seems to be more susceptible to this disease than other varieties, because its very tight
bunches prevent the interior grapes in the bunch from drying out.
The fungus overwinters on leaves and fallen fruit on the vineyard floor. Under moist
conditions in the spring, the spores of this fungus can infect the grape flowers, young
shoots, and young leaves. Symptoms of bunch rot are evident when the cluster turns brown
or the skin slips off the berry. The characteristic sign of bunch rot is a fluffy, gray-brown
